This is directed, in general, to projection visual display (PVD) systems and, more specifically, to a system and method employing a diffuser that moves the diffuser in a particular manner to reduce visible speckle that may be evident in such systems.
Televisions and other types of imaging systems are pervasive in today's society. Recent years have seen the introduction of higher definition imaging systems. Engineers continue to try to increase the resolution and brightness of imaging systems to provide better picture quality, but also face constraints associated with providing such increased resolution and brightness.
For example, to increase brightness in PVD systems, coherent light sources such as lasers may be used in the place of incoherent light sources such as light-emitting-diodes (LEDs) and incandescent or fluorescent lamps. However, while coherent light sources may increase the brightness of the PVD system, such light sources often produce images having a noticeable granularity. This grainy pattern, also known as speckle or the scintillation effect, arises due to the highly narrowband and polarized nature of the coherent light incident on a diffuse surface.
Speckle has been attributed to the fact that coherent light reflected by or through a diffuser produces a complex, random, but stationary diffraction pattern. Specifically, speckle originates when the coherent plane phase front from a laser scatters within a medium with optical path length differences that are less than or equal to the coherence length of the laser. Speckle scattering optical material is used in projection displays at the screen in order to expand the viewing angle. Within the illumination system scattering or diffusing material is needed to distribute the light over the area of the spatial light modulator. Speckle can also rise from path length differences as a result of surface roughness, scratches, digs and polishing imperfections in optical elements.